JP3338277B2 - Method for producing nickel electrode active material for alkaline storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a nickel electrode active material for an alkaline storage battery, and more particularly to a method for producing an active material used for a non-sintered nickel electrode.

[0002]

2. Description of the Related Art A nickel electrode for an alkaline storage battery is filled with an active material mainly composed of nickel hydroxide. In addition to a conventionally used sintered nickel electrode, a powder of the active material is used. Non-sintered nickel electrodes are also known, which are filled in a substrate such as foamed nickel, or made into a paste and held on a punching metal or the like.

[0003] The nickel electrode is used as a positive electrode of an alkaline storage battery such as a nickel-cadmium secondary battery or a nickel-hydrogen secondary battery. There is a great demand for capacity. In terms of increasing the capacity of a battery, the non-sintered type is advantageous in that the packing density of the active material can be increased as compared with the sintered type, but the utilization rate of the active material tends to be low. Attempts have been made to further increase the capacity by improving the capacity.

Techniques for improving the utilization rate of the active material include adding cobalt or a cobalt compound to particles mainly composed of nickel hydroxide, depositing and coating a cobalt compound on the surface of the particles, It is conventionally known to coat with a cobalt compound and then oxidize with a hydrogen peroxide solution. When the nickel positive electrode plate thus filled with the active material containing cobalt or a cobalt compound is incorporated into an alkaline storage battery, the cobalt species is once dissolved in the electrolytic solution and uniformly dispersed on the surface of the nickel hydroxide.
By subsequent initial charging, deposition is performed in a state where the active material and the active material and between the active material and the current collector are connected. This precipitate becomes cobalt oxyhydroxide, and the conductivity between the active material and the active material and between the active material and the current collector are improved by the conductive network of the cobalt oxyhydroxide, thereby increasing the utilization rate of the active material. It is thought to improve.

However, even when a positive electrode is filled with such a nickel active material containing a cobalt species to produce a battery, at the time of overdischarge, the cobalt compound enters the nickel hydroxide particles and the effect of the cobalt compound is lost. As a result, there is a problem of overdischarge characteristics that the improvement of the utilization rate is not sustained. On the other hand, Japanese Patent Application No. 6-2 filed by the present inventors has
In 25104, nickel hydroxide particles whose surface is coated with a cobalt compound are further heat-treated in an oxygen atmosphere in which an alkali coexists (hereinafter, referred to as an alkali heat treatment), whereby a higher order valence of more than 2 is obtained. Forming a cobalt oxide on the surface of the nickel hydroxide particles, thereby increasing the effect of improving the conductivity, changing the state of the pores of the nickel hydroxide particles, and improving the overdischarge characteristics. showed that.

Here, as a specific method of the alkali heat treatment, a method has been shown in which particles whose surfaces are coated with a cobalt compound are impregnated with an aqueous alkali solution, and then the impregnated particles are heated in air.

[0007]

However, in the case of such a treatment method, in a heating step, a plurality of nickel hydroxide particles are causticized by a cobalt compound to form a particle mass, and the produced active material is not treated. However, there is a problem that a particle mass is included.

[0008] It is difficult to fill an active material containing a particle mass into a positive electrode such as foamed nickel as it is. Therefore, although this was used after pulverization, the cobalt compound on the surface was partially peeled off at the time of pulverization, and the effect of improving the utilization during high-rate discharge by the cobalt compound subjected to alkali heat treatment was impaired. become. In view of the above problems, the present invention provides a method for producing a nickel active material by subjecting a nickel compound having a cobalt compound disposed on the surface to alkaline heat treatment, by suppressing the occurrence of particle clumps due to caking of particles. An object of the present invention is to improve battery characteristics such as an active material utilization rate and a high-rate discharge characteristic in an alkaline storage battery.

[0009]

In order to solve the above-mentioned problems, the present invention provides a method in which an aqueous alkaline solution is mixed with particulates having a cobalt compound disposed on the surface of particles mainly composed of nickel hydroxide. An alkali mixing step and heating the granules mixed with the aqueous alkali solution in the presence of oxygen
The nickel hydroxide is the main component
And a heating step of increasing the order of the cobalt compound on the surface of the particles.In the method for producing a nickel electrode active material for an alkaline storage battery , the heating step includes heating while flowing or dispersing the particulate matter mixed with the alkaline aqueous solution. I do. Alternatively, in an alkali mixing step, an alkaline aqueous solution is sprayed while the granules are flown or dispersed in heated air.

In the conventional method of heating by impregnating with an aqueous alkali solution, the cobalt compound partially dissolves in the aqueous alkali solution adhered to the granular material during heating, and as the cobalt compound is reprecipitated, the adjacent granular material is re-precipitated. Is caking,
As in the production method of the present invention, when heating while flowing or dispersing the granules mixed with the alkaline aqueous solution, when the cobalt compound is reprecipitated, it is prevented that adjacent particles are caking, and Lump formation is suppressed. Further, when the alkaline aqueous solution is sprayed while the granular material is flowed or dispersed in the heated air, the alkaline aqueous solution attached to the particles is immediately dried, and the adjacent particles are not adhered.

Therefore, according to the production method of the present invention, since the falling of the cobalt compound accompanying the pulverization of the particle mass, which has conventionally occurred when filling the positive electrode, is prevented, the active material obtained by the conventional production method can be reduced. Active material utilization and high rate discharge characteristics are improved. Here, the following can be performed in order to further suppress the generation of the particle mass and to produce a better active material.

In the alkali mixing step, the particulate matter is held on a porous holding member, and spraying an aqueous alkali solution from below the holding member while passing a hot air flow from the holding member provides an effect of suppressing the generation of particle clumps. Increase. Here, the treatment can be performed more efficiently by performing the stirring while mechanically stirring the granular material on the holder. Regarding the granular material to be used, the content of the cobalt compound with respect to nickel hydroxide is from 1% by weight in terms of cobalt hydroxide.
The content of 14% by weight is preferable from the viewpoint of the active material utilization rate and the like.

In the alkali mixing step, it is preferable to use an alkali aqueous solution of 10% by weight to 40% by weight from the viewpoint of active material utilization and the like. The heating temperature of the alkali heat treatment is preferably from 40 ° C. to 150 ° C. from the viewpoint of the active material utilization rate and the like.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing an active material of the present invention will be specifically described. (Embodiment 1) A mixed aqueous solution of nickel sulfate, zinc sulfate, and cobalt sulfate was adjusted so that a molar ratio of nickel to zinc was 0.02 and cobalt to 0.02, and water was stirred while stirring. A sodium oxide solution is gradually added dropwise to stabilize the pH to 13 to 14 during the reaction, thereby precipitating nickel hydroxide crystals. Trace amounts of zinc and cobalt are dissolved in the precipitated nickel hydroxide crystals.

Next, an aqueous solution of cobalt sulfate having a specific gravity of 1.30 and an aqueous solution of 25% by weight of sodium hydroxide are added dropwise while stirring the aqueous solution in which the crystals of nickel hydroxide are precipitated, so that the pH is maintained at 9 to 10. As a result, granules having nickel hydroxide crystals as nuclei and cobalt hydroxide precipitated on the surface thereof are generated. The amount of cobalt hydroxide deposited on the surface of the nickel hydroxide, that is, the content of cobalt hydroxide in the generated particulate matter, was aged by maintaining the concentration of the aqueous solution of cobalt sulfate to be dropped and the pH at 9 to 10. By adjusting the time for the addition, the amount can be adjusted to a predetermined amount.

The granules are separated, washed with water and dried.
Then, the granular material is subjected to an alkali heat treatment by spraying an alkaline aqueous solution onto the granular material while stirring in a hot air flow as described below, thereby producing an active material. FIG.
It is the schematic of the fluidized-granulation apparatus used by this Embodiment. Here, as the fluidized-granulation device 1, a multifunctional fluidized-drier Agromaster (Agromaster is a trade name) manufactured by Hosokawa Micron Corporation is used.

This fluidized-granulation apparatus 1 comprises a cylindrical apparatus upper part 1a and a cylindrical apparatus lower part 1b having a larger diameter than that of the apparatus. The entire apparatus is surrounded by an exterior plate 2 and air flows vertically. I can do it. In the center of the lower part 1b of the apparatus, a stirring blade 3 for stirring the granular material is installed.
Immediately below this, a mesh disk 4 (2 μm) for preventing the falling of the granular material is attached. Also the lower part 1 of the device
At the lower end of b, a hot air inlet 5 for taking in hot air sent from an external hot air blower (not shown) is provided, and at the upper end, an inlet 6 for introducing granular materials into the apparatus is provided.

A spray nozzle 7 for spraying the liquid to the agitated particulate matter is installed in the upper part 1a of the apparatus, and air is supplied from the apparatus 1 to an upper end of the upper part 1a by an external suction device (not shown). An air outlet 8 for discharging is provided. In addition, a spray nozzle 7 is provided outside the exterior plate 2.
A pump 9 for feeding an alkaline aqueous solution is provided.

An example of the alkali heat treatment performed using the fluidized granulation apparatus 1 will be described below. The nickel hydroxide particles having cobalt hydroxide precipitated on the surface are charged through the charging port 6. The charged granular material is stored on the mesh disk 4 in the lower part 1b of the apparatus. When hot air is sent from the outside to the hot air inlet 5 and air is taken in from the air outlet 8 to the outside, as shown by the white arrow in FIG.
Ascend through. At this time, the granular material on the mesh disk 4 is heated by the rising hot air.

When the stirring blade 3 is further rotated, the granular material on the mesh disk 4 is stirred. In this state, the granular material on the mesh disk 4 is in a state where it is agitated in hot air and dispersed in the hot air, and a part of the granular material is blown up by the hot air, and the lower part 1b of the device and Upper device 1a
It is in a state of being diffused inside.

Subsequently, the pump 9 is operated to spray a predetermined amount of the alkaline aqueous solution from the spray nozzle 7. The sprayed alkaline aqueous solution adheres to the surface of the granular material blown up by hot air or the granular material stirred by the stirring blade 3, and permeates the cobalt hydroxide on the particle surface. By the time the alkaline aqueous solution is completely sprayed, the alkaline aqueous solution uniformly adheres and permeates on the entire surface of the granular material, and by the action of the attached alkaline aqueous solution and the heated air,
The order of cobalt hydroxide on the particle surface is increased.

The amount of intake air and the amount of hot air blown are controlled so that the particulate matter is blown up and dispersed and diffused. The temperature of the hot air is controlled by the temperature of the airflow around the stirred particulate matter, that is, the heat treatment temperature is a predetermined heat treatment temperature. Control so that temperature is maintained. The amount of the aqueous alkali solution to be sprayed is
The setting is made so that the alkaline aqueous solution adheres appropriately to the entire surface of the granular material and is impregnated. Here, an aqueous sodium hydroxide solution in which 5 parts by weight of sodium hydroxide is dissolved in an appropriate amount of water with respect to 95 parts by weight of the granular material is used. For example, 2
In the case of a 5% by weight aqueous solution of sodium hydroxide, an aqueous solution of sodium hydroxide obtained by dissolving 5 parts by weight of sodium hydroxide in 15 parts by weight of water is used.

Then, the alkali aqueous solution is sprayed for about 10 minutes, and after the spraying is completed, the alkali heat treatment is completed by continuing stirring in a hot air stream for about 15 minutes. Thereafter, the apparatus is stopped, and the granular material subjected to the alkali heat treatment, that is, the produced active material is taken out from the inlet 6.

The amount of cobalt contained in the produced active material can be measured as follows. The active material is dissolved in acidic water, and the ratio of Ni and Co in this solution is analyzed by an ICP emission spectrometer. Assuming that the active material is formed of nickel hydroxide and cobalt hydroxide, the weight percent of cobalt hydroxide relative to the weight of the entire active material was calculated based on the measured ratio of Ni and Co, and this value was calculated. Is the amount of cobalt.

The average oxidation number of the higher order cobalt oxide can be measured as follows. It can be seen that the cobalt oxide that has been made higher by the alkali heat treatment is a mixture of divalent and trivalent cobalt oxides. Here, a bivalent cobalt oxide is dissolved in nitric acid, but a trivalent cobalt oxide is hardly dissolved in nitric acid.

First, a predetermined amount of the granular material subjected to the alkali heat treatment is washed with a hydrochloric acid solution, and the amount of cobalt eluted in the washing solution is measured by ICP to obtain a divalent cobalt content. Next, the same amount of the granular material subjected to the alkali heat treatment was washed with a nitric acid solution, and the amount of cobalt eluted in the washing solution was determined by IC.
Measured by P to give the total cobalt content. The difference between the total cobalt content and the divalent cobalt content is defined as the trivalent cobalt content.

The average oxidation number is determined from the divalent cobalt content and the trivalent cobalt content thus determined. Note that, in the present embodiment, the method of performing the alkali heat treatment while stirring the granular material with the stirring blade has been described.However, with the same apparatus, when the amount of the granular material is small, the granular material is used without using the stirring blade. It can be carried out even when stirring is performed by blowing up with a hot air flow.

(Embodiment 2) In the same manner as in Embodiment 1, granules having nickel hydroxide crystals as nuclei and cobalt hydroxide precipitated on the surface thereof are produced. Then, an alkaline heat treatment is performed by spraying an alkaline aqueous solution while stirring the produced granular material with a kneader while heating, thereby producing an active material.

FIG. 2 shows a kneader 10 used in the present embodiment.
FIG. The kneader 10 is configured such that two blades 12 in the container body 11 are rotated in opposite directions by a motor 13 so that the particulate matter and the like in the container body 11 can be mixed. A spray nozzle 14 for spraying an alkaline aqueous solution is attached to the upper part of the side wall of the container body 11. A heater 15 is attached to the outer surface of the container body 11. Container body 11
Has an opening / closing cover 16 attached thereto. Further, the container body 11 is supported by the kneader support 17 in a reversible manner.

An example of the alkali heat treatment using the kneader 10 will be described below. First, a granular material is charged from the opening 11a of the container body 11. At this time, it is necessary that the charged amount is such that the upper surface of the charged granular material is lower than the spray nozzle 14. The container body 11 is heated by the heater 15 while the opening / closing cover 16 is closed and the blade 12 is rotated. When the blade 12 rotates, the granular material is
Adjust so as to be appropriately dispersed within 1.

When the inside of the container body 11 reaches a predetermined heat treatment temperature, an aqueous alkali solution is sprayed from the spray nozzle 14. Thereby, an aqueous alkali solution is sprayed on the granules in a state where the granules are dispersed while flowing in the heated air. The spray amount is set in the same manner as in the first embodiment. After completion of the spraying, the alkali heat treatment is completed by continuing stirring in a hot air stream for about 15 minutes.

Thereafter, the blade 12 is stopped, the opening / closing cover 16 is opened, and the container body 11 is turned over to take out the particulate matter. (Embodiment 3) In the same manner as in Embodiment 1, granules having nickel hydroxide crystals as nuclei and cobalt hydroxide precipitated on the surface thereof were produced. Then, the produced granular material is
Alkaline heat treatment was performed by spraying an alkaline aqueous solution while stirring with a mixer while flowing hot air to produce an active material.

FIG. 3 is a schematic diagram of the mixer 20 used in the present embodiment. Here, as the mixer 20, Nautamixer (Nautamixer is a trade name) manufactured by Hosokawa Micron Corporation is used. In the mixer 20, a swing arm 22 and a screw 23 that rotates while revolving along with the rotation of the swing arm 22 are mounted in a conical container 21, and the swing arm 22 and the screw 23 are rotated by a motor 29 . It is designed to rotate. A spray nozzle 24 for spraying an alkaline aqueous solution is attached to the tip of the swing arm.

A cover 25 for covering the upper opening of the container 21 has a blowing port 26 for blowing hot air into the container 21,
A supply port 27 for supplying the granular material is provided.
In addition, a discharge port 28 is provided at the lower end of the container 21 so that the contents in the container 21 can be continuously discharged. A heater (not shown) is attached to the outer surface of the container 21.

The spray nozzle 24 has a cover 2
An alkaline aqueous solution is sent from the outside of the swing arm 5 through the inside of the swing arm 22. An example of the alkali heat treatment using the mixer 20 will be described below.
The container 21 is heated by the heater, and hot air is blown from the blower port 26 to maintain the inside of the container 21 at a predetermined heat treatment temperature.

While rotating the swing arm 22 and the screw 23 to spray the alkaline aqueous solution from the spray nozzle 24, the granular material is continuously charged from the supply port 27 and continuously discharged from the discharge port 28. In the container 21, the granular material is stirred in the heated air by the screw 23, and a part thereof is sprayed while being dispersed in the heated air by the screw 23.

Here, the amount of the particulate matter retained in the container 21 is adjusted to be about 20% with respect to the volume of the container 21. The supply amount of the granular material per unit time is determined by the time required for completing the alkaline heat treatment of the granular material (for example, 2 times).
(0 min), the adjustment is performed so that the particulate matter stays in the container 21. The spray amount of the aqueous sodium hydroxide solution is the same as in the first embodiment.
Adjust so that it is the same as.

Thus, the granular material is continuously subjected to the alkali heating treatment. (Embodiment 4) In the present embodiment, the mixing of the aqueous sodium hydroxide solution with the particulate matter is performed not by spraying in heated air but by immersion, and thereafter, while flowing in heated air, Heat treatment is performed.

That is, in the same manner as in the first embodiment, nickel hydroxide particles having cobalt hydroxide precipitated on the surface are produced. Then, collect the prepared granules, wash them with water,
After being dried and immersed in an aqueous sodium hydroxide solution, the solution was dried.
The alkaline heat treatment is performed by heating with stirring in a beaker for 5 hours.

[0040]

【Example】

(Example 1) According to the method of Embodiment 1, the water content of the granular material at the time of preparation was about 10% by weight, the concentration of the aqueous sodium hydroxide used for the alkali heat treatment was 25% by weight, the heat treatment temperature was 80 ° C, and the amount of cobalt was Prepared an active material A1 under the condition of 10% by weight (see Table 1).

Observation of the active material thus produced revealed that the particles had the same size and that almost no particle mass was formed. This active material is 100 mesh (150
μm). (Example 2) According to the method of Embodiment 2, the water content of the granular material at the time of charging is about 10% by weight, the charging amount of the granular material is about 40% with respect to the volume of the container body 11, and the rotation speed of the blade 12 The active material A2 was prepared under the conditions of about 10 rpm, the concentration of sodium hydroxide used for the alkali heat treatment was 25% by weight, the heating temperature was 80 ° C., and the amount of cobalt was 10% by weight.

When the active material thus produced was observed, it was found that the particles had the same size and almost no particle mass was formed. When this active material was sieved with 100 mesh, the remaining amount was 1% or less. (Example 3) According to the method of Embodiment 3, the water content of the granular material at the time of preparation was about 10% by weight, the rotation speed of the screw 23 was about 20 rpm, the concentration of sodium hydroxide used for the alkali heat treatment was 25% by weight, An active material A3 was prepared under the conditions that the heating temperature was 80 ° C. and the amount of cobalt was 10% by weight.

Observation of the active material thus produced revealed that the particles had the same size, and almost no particle mass was formed. This active material was sieved through a 100-mesh sieve, and the remaining amount was measured to be 1% or less. (Example 4) According to the method of Embodiment 4, the alkali heat treatment was performed under the conditions that the concentration of sodium hydroxide used in the alkali heat treatment was 25% by weight, the heating temperature was 80 ° C, and the amount of cobalt was 10% by weight. Observation of the granular material thus treated revealed that a plurality of particles clumped together and appeared to be formed. The residual amount was measured by sieving this granular material through a 100-mesh sieve and found to be 5% or less.

The granular material is pulverized with a pulverizer so that the active material A4 can be filled in the positive electrode.
Was prepared. Observation of the active material A4 with a SEM photograph revealed that the cobalt compound layer on the surface was partially peeled off. (Example 5) According to the method of Embodiment 1, the water content of the granular material at the time of preparation was about 10% by weight, the concentration of the aqueous sodium hydroxide used for the alkali heat treatment was 25% by weight, and the heat treatment temperature was 80 ° C. , Cobalt content is 0.5-16
The active material B0, B1, B2, B
3, B4, B5, B6, and B7 were produced (see Table 2).

Observation of the active material thus produced showed that the particles were uniform in size and almost no particle mass was formed. (Example 6) According to the method of Embodiment 1, the water content of the granular material at the time of preparation was about 10% by weight, the heat treatment temperature was 80 ° C,
Under the condition that the amount of cobalt is 10% by weight, the concentration of the aqueous solution of sodium hydroxide used for the alkali heat treatment is changed in the range of 7 to 45% by weight, and the active materials C0, C1, C2, C3, C
4, C5 were produced (see Table 3).

Observation of the active material thus produced revealed that the particles had the same size, and almost no particle mass was formed. (Example 7) According to the method of Embodiment 1, the water content of the granular material at the time of preparation is about 10% by weight, the concentration of the aqueous sodium hydroxide used for the alkali heat treatment is 25% by weight, and the amount of cobalt is 10% by weight. And the heat treatment temperature is 35-1.
The active materials D0, D1, D2, D3,
D4, D5 and D6 were produced (see Table 4).

The active material A of the embodiment thus prepared
1, A2, A3, B0 to B7, C0 to C5, and D0 to D6 all had nickel hydroxide particles as nuclei and a higher-order cobalt oxide having a valence of more than 2 was present on the surface. It is considered that the state of the pores of the nickel hydroxide has been changed to a state that improves the overdischarge characteristics by the alkali heat treatment due to the particle structure.

When the active material thus produced was observed, it was found that the particles had the same size and almost no particle mass was formed. (Comparative Example) In the same manner as in Embodiment 1, nickel hydroxide particles having cobalt hydroxide precipitated on the surface were produced.

The prepared granules are collected, washed with water, dried, immersed in a 25% aqueous sodium hydroxide solution, spread evenly on filter paper, and heated to 80 ° C. for 0.5 hours. Alkali heat treatment was performed. Observation of the granular material thus treated revealed that a large number of particle agglomerates were present. The residual amount was measured by sieving this granular material through a 100-mesh sieve, and it was about 50%.

Thus, the granular material was pulverized by a pulverizer to prepare an active material Y. The cobalt amount of the active material Y was 10% by weight. When the active material Y was observed with a SEM photograph, it was found that the cobalt compound layer on the surface was partially peeled off. (Experimental part) When the average oxidation number of each of the active materials of the above Examples and Comparative Examples was measured by the method described in Embodiment 1, almost the same value (about 2.9) was obtained. . The average oxidation number of the standard cobalt hydroxide crystal was measured by the same measurement method and found to be 2.0. In addition, when confirmed by the electrochemical method,
Similar results were obtained.

From this, it is judged that the majority of the cobalt hydroxide on the particle surface of all active materials was converted to trivalent cobalt oxide by alkali heat treatment. The following unipolar test and battery performance test were performed using the active materials of the above Examples and Comparative Examples. * Unipolar test (1) Measurement of electrode plate utilization rate 100 parts by weight of each active material and 50 parts by weight of a 0.2% by weight aqueous solution of hydroxypropylcellulose are mixed to prepare an active material slurry liquid.

The slurry of the active material was used for porosity 95%,
After filling into 1.6mm thick foamed nickel and drying,
Rolling to a thickness of 0.60 mm produces a test nickel electrode. Here, the filling amount of the active material is calculated from the theoretical capacity of nickel hydroxide contained in the active material, and is set so that the theoretical capacity of the electrode becomes 1200 mAh. And
With respect to the nickel electrode for each test, an open-type simple cell is prepared using an approximately 25% by weight aqueous KOH solution using a nickel plate as a counter electrode, and charged at 120 mA for 24 hours. Next, the nickel plate is discharged at 400 mA until the discharge end voltage becomes -0.8 V, and the discharge capacity is measured. Then, the electrode plate utilization rate is calculated by the following equation.

Electrode utilization rate = measured discharge capacity / theoretical capacity of electrode * Battery performance test A test battery is prepared using each active material, and a battery performance test is performed. For the positive electrode, a positive electrode having a nominal capacity of 1200 mAh is manufactured by the same manufacturing method as the above-described manufacturing method using the electrode plate. However, the weight of the active material to be charged into the positive electrode is common, and is calculated from the nominal capacity on the assumption that the active material consists of only nickel hydroxide.

The negative electrode is manufactured as follows. Misch metal (Mm), nickel, cobalt, aluminum and manganese are added in 1.0: 3.6: 0.6: 0.2: 0.
The mixture is mixed at a ratio of 6 to obtain a molten alloy in a high-frequency induction furnace in an argon gas atmosphere. Then, the molten alloy is cooled, and the composition formula thereof is Mm _1.0 Ni _3.6 Co _{0.6 Al0.2} Mn _0.6
To produce an ingot represented by This ingot is pulverized to produce a hydrogen storage alloy having an average particle diameter of about 100 μm.

A binder such as polyethylene oxide and an appropriate amount of water are added to the hydrogen storage alloy and mixed to prepare a hydrogen storage alloy paste, which is applied to both surfaces of a punching metal.
After drying, the negative electrode is prepared by rolling to a thickness of 0.4 mm. Furthermore, using each of the positive electrodes and the common negative electrode thus produced, a positive electrode and a negative electrode are stacked via a separator to form an electrode group formed by spirally winding,
It is housed in a cylindrical outer can and impregnated with an alkaline electrolyte to produce a cylindrical sealed nickel-hydrogen storage battery (AA size). In addition, as an alkaline electrolyte, 7
A KOH aqueous solution of up to 8.5 N is used, and a nylon nonwoven fabric is used as the separator. The theoretical capacity of the battery is defined by the positive electrode, and the capacity of the negative electrode is set to be larger and about 1.5 times.

(1) Measurement of Capacity per Unit Active Material Each test battery is charged at 120 mA for 16 hours. Next, discharge is performed at 240 mA until the discharge end voltage reaches 1.0 V, and the discharge capacity is measured. Then, the capacity per unit active material is calculated by the following equation. Capacity per unit active material = measured discharge capacity / active material weight (The active material weight refers to the weight of the entire active material including the cobalt compound etc.) (2) High rate discharge characteristics (a) 2C discharge test Battery is charged at 120 mA for 16 hours. Next, discharge is performed at 2400 mA until the discharge end voltage becomes 1.0 V, and the discharge capacity is measured.

(B) 4C discharge The batteries for each test are charged at 120 mA for 16 hours. Next, discharge is performed at 4800 mA until the discharge end voltage becomes 1.0 V, and the discharge capacity is measured. [Test results and discussion]

[0058]

[Table 1] Table 1 shows the results of (1) the capacity per unit active material and (2) the high rate discharge characteristics of the battery performance tests for the active materials A1, A2, A3, and A4 of the example and the active material Y of the comparative example. It is shown.
The numerical values in Table 1 are based on the value for the active material Y as the reference value 1.
00 and the ratio to this is shown.

From the results shown in Table 1, the active materials A1 and A
2, A3 and A4 show higher values of the capacity per unit active material and the high rate discharge characteristics as compared with the active material Y of the comparative example.
It can be seen that when heat-treating particles mixed with an alkaline aqueous solution in heated air, it is preferable to perform the treatment while stirring, that is, while flowing the particles. Active material A
1, A2, and A3 can be said to have higher values of the capacity per unit active material and the high-rate discharge characteristics than the active materials A4 and Y.

The active materials A1, A2, and A3 are such that in each particle, the entire surface of the nickel hydroxide crystal nucleus is covered with high-order cobalt oxide, and there is almost no particle agglomerate, and the positive electrode is not pulverized. When used for the positive electrode of a battery, the formation of a conductive network by high-order cobalt oxide is good, while the active material A4, Y
Required grinding, the higher-order cobalt oxide that covered the surface of the nickel hydroxide crystal nuclei dropped off, and when used for the battery's positive electrode, the function of the conductive network was reduced accordingly. It is thought that it was done.

When the active materials A1, A2 and A3 are compared with each other, there is almost no difference in the capacity per unit active material. However, regarding the high rate discharge characteristics, the active material A1 is the highest, followed by the active material A2 and the active material. The order is A3. This is because the dispersion and diffusion of the particulate matter into the heated air when spraying the alkaline aqueous solution is best in the first embodiment, and then in the order of the second and third embodiments. It is considered that

When comparing the active material A 4 with the active material Y, the active material A 4 has a higher capacity per unit active material and a higher rate discharge characteristic than the active material Y. This is the same as immersing the granular material in the aqueous sodium hydroxide solution, but the active material A4
When the treatment is carried out while stirring in heated air as in the above, since the degree of generation of the particle mass is smaller than in the case where the treatment is carried out without stirring in heated air as in the case of the active material Y, the higher order cobalt oxide accompanying the grinding is obtained. This is probably due to little peeling of the film.

[0063]

[Table 2] Table 2 shows the active materials B0, B1, B2, B3, and B of Example 5.
Regarding 4, B5, B6 and B7, the results of (1) electrode plate utilization of the monopolar test are shown. In addition, the value of the electrode plate utilization rate in Table 2 is shown as a ratio with respect to the value of the same active material B4 as the active material A1 as the reference value 100.

The electrode utilization rates of the active materials B1, B2, B3, B4, B5, and B6 are higher than the electrode utilization rates of the active materials B0 and B7. This indicates that the range of 1 to 14% by weight of the cobalt content of the active material is good.
This is because when the cobalt content is less than 1% by weight, it is impossible to secure a sufficient conductive network, which leads to a decrease in the utilization rate of the electrode plate. When the cobalt amount exceeds 14% by weight, nickel hydroxide in the active material is used. It is probable that the decrease in the amount ratio affected the decrease in the electrode plate utilization rate.

[0065]

[Table 3] Table 3 shows the active materials C0, C1, C2, C3, and C of Example 6.
For 4,5, the results of (1) electrode plate utilization of the monopolar test are shown. In addition, the numerical value of the electrode plate utilization rate in Table 3 is shown as a ratio with respect to the value of the active material C2 which is the same as the active material A1 as a reference value 100.

The electrode utilization rates of the active materials C1, C2, C3, and C4 are higher than the electrode utilization rates of the active materials C0 and C5. This shows that the concentration of sodium hydroxide to be sprayed is preferably in the range of 10% by weight to 40% by weight. If the amount is less than 10% by weight, the action of the alkaline aqueous solution to dissolve the cobalt hydroxide is weak, so that the action of producing higher-order cobalt oxide is weak. If it exceeds 40% by weight, the viscosity of the alkaline aqueous solution is high. This is probably because the permeability to the active material is weak and the action of generating higher-order cobalt oxide is weak.

[0067]

[Table 4] Table 4 shows the active materials D0, D1, D2, D3, and D of Example 7.
For 4, D5 and D6, the results of (1) electrode plate utilization of the monopolar test are shown. The value of the electrode plate utilization rate in Table 4 is based on the value of the same active material D3 as the active material A1 and the reference value is 100
And the ratio to this is shown.

The electrode utilization rates of the active materials D1, D2, D3, D4, and D5 are higher than the electrode utilization rates of the active materials D0 and D6. From this, the heat treatment temperature is from 40 ° C. to 1
It turns out that the range of 50 ° C. is appropriate. This is 40
When the temperature is lower than 0 ° C, the strength of the alkaline aqueous solution to dissolve cobalt hydroxide is weak, and the action of generating higher-order cobalt oxide is weak. When the temperature exceeds 150 ° C, the structure of nickel hydroxide itself changes and the active material is changed. This is probably due to deterioration.

In the above experiment, an example was shown in which the test was conducted by filling the active material into foamed nickel. However, similar results can be obtained when a paste-type electrode is produced from the active material and tested. It is considered something. (Other Matters) In the first to third embodiments,
After the completion of the spraying of the aqueous alkali solution, a further heat treatment was performed to complete the alkali heat treatment, but such a step is not essential to the present invention.

Further, the production method of the present invention is not limited to the above-described embodiment, and the alkali heat treatment may be performed while flowing or dispersing the granular material mixed with the alkaline aqueous solution. For example, the method can be carried out by spraying an alkaline aqueous solution through a hot air stream while stirring the particulate matter in a rotating drum. Further, in the above-described embodiment, an example is shown in which an alkaline heat treatment is performed using a granular material obtained by depositing cobalt hydroxide on the surface of nickel hydroxide crystals in which trace amounts of zinc and cobalt are dissolved, The same can be applied to the case where cadmium or the like is contained in the crystal of nickel oxide. In addition, in general, the present invention can be similarly performed as long as it is a granular material in which a cobalt compound is arranged on the surface of particles mainly composed of nickel hydroxide.

In the above embodiment, an example was given in which an aqueous sodium hydroxide solution was used as the aqueous alkali solution used for the alkali heat treatment. However, an aqueous potassium hydroxide solution or the like was used, or an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution was used. Even if a small amount of lithium hydroxide is used,
Can be implemented.

[0072]

As described above, according to the method for producing an active material of the present invention, it is possible to prevent the generation of particle clumps due to the caking of particles when the nickel hydroxide on which the cobalt compound is disposed is subjected to alkali heat treatment. Therefore, the peeling of the cobalt compound accompanying the pulverization of the particle mass can be suppressed.

Therefore, as compared with an active material manufactured by a conventional alkaline heat treatment method, battery characteristics such as an active material utilization rate and a high-rate discharge characteristic of an alkaline storage battery can be improved. Further, in the production method of the present invention, it is possible to continuously perform the alkali heat treatment. Thus, the present invention is a valuable technology for increasing the capacity of an alkaline storage battery.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a fluidized-granulation apparatus according to Embodiment 1.

FIG. 2 is a schematic view of a kneader according to a second embodiment.

FIG. 3 is a schematic diagram of a mixer according to a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fluid granulation apparatus 3 Stirring blade 4 Mesh disk 7 Spray nozzle 10 Kneader 12 Blade 14 Spray nozzle 20 Mixer 22 Swing arm 23 Screw 24 Spray nozzle

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-200555 (JP, A) JP-A-63-48746 (JP, A) JP-A-59-16269 (JP, A) 500730 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 4/24-4/52

Claims (8)

(57) [Claims] Respect 1. A comprising cobalt compound is disposed on the surface of the particles mainly composed of nickel hydroxide granules, an alkali mixing step of mixing the aqueous alkaline solution, Al
Heat the granular material mixed with potassium aqueous solution in the presence of oxygen
The nickel hydroxide is the main component
And a heating step of increasing the order of the cobalt compound on the surface of the particles , wherein the heating step includes heating while flowing or dispersing the particulate matter mixed with the alkaline aqueous solution. A method for producing a nickel electrode active material for an alkaline storage battery. 2. An alkali mixing step of mixing an alkaline aqueous solution with a granular material comprising a cobalt compound disposed on the surface of particles mainly composed of nickel hydroxide, and a step of mixing the granular material mixed with the alkaline aqueous solution with oxygen. Heating in the presence
The nickel hydroxide is the main component
And a heating step of increasing the order of the cobalt compound on the surface of the particles.The method for producing a nickel electrode active material for an alkaline storage battery, wherein in the alkali mixing step, the granules are alkalized while flowing or dispersing the particles in heated air. A method for producing a nickel electrode active material for an alkaline storage battery, comprising spraying an aqueous solution. 3. The method for producing a nickel electrode active material for an alkaline storage battery according to claim 1, wherein in the alkali mixing step, an alkaline aqueous solution is sprayed while flowing or dispersing the particulate matter in heated air. 4. The method according to claim 2, wherein, in the alkali mixing step, the particulate matter is held on a porous holding body, and sprayed while passing a hot air flow from below the holding body. Of producing a nickel electrode active material for an alkaline storage battery. 5. The method for producing a nickel electrode active material for an alkaline storage battery according to claim 4 , wherein, in the alkali mixing step, the granular material is sprayed on the holding member while mechanically stirring. 6. The granular material according to claim 1, wherein the content of the cobalt compound with respect to nickel hydroxide is 1% by weight to 14% by weight in terms of cobalt hydroxide.
6. The method for producing a nickel electrode active material for an alkaline storage battery according to any one of claims 1 to 5. 7. The method for producing a nickel electrode active material for an alkaline storage battery according to claim 1, wherein the concentration of the aqueous alkali solution mixed in the alkali mixing step is 10% by weight to 40% by weight. 8. The heating temperature in the heating step is 40.
The method for producing a nickel electrode active material for an alkaline storage battery according to any one of claims 1 to 5, wherein the temperature is from 0C to 150C.